The invention relates to a detectable warning system. More particularly, the invention relates to a system for easily and effectively creating a field installation of prefabricated detectable warnings to pavement using thermoplastic to provide a tactile warning to pedestrians regarding a hazardous transition.
It is well known that persons with little or no usable vision depend upon environmental cues—ambient sounds, edges and other physical elements that can be sensed by a cane, and texture changes underfoot—for safe and independent travel. People with low vision can also use color contrast as a navigation aid. When raised curbs do not mark and separate the pedestrian route on a sidewalk from the vehicular way, as at curb ramps, vehicle drop-offs, or depressed corners at intersections, it is difficult for some pedestrians to discern the boundary between pedestrian safety and hazard.
Because of the inherent danger caused by transitions without textural changes, the Americans with Disabilities Act Accessibility Guidelines (ADAAG) requires that detectable warnings be installed onto pavement or ground surfaces at certain hazardous junctures. The detectable warnings provide a contrasting texture that signals a hazardous condition to the pedestrian, and thereby informs the pedestrian to exercise care. In particular, the current regulation requires that the detectable warning consist of truncated domes having a nominal diameter of 0.9 inches, protruding from the ground surface to a height of 0.2 inches, and having a center-to-center spacing of 2.35 inches. In addition, the warning should be of contrasting color to effectively warn those who have greatly reduced vision.
In many cases, the warnings must be retrofitted onto existing ground surfaces. Further, the installation of such warnings is not readily compatible with standard paving techniques. Accordingly, the detectable warnings are most typically installed onto already existing pavement surfaces.
Some have proposed systems for the creation and installation of the domes. Generally these systems involve the use of templates to create the dome “in place”. Others have proposed systems of prefabricated warning domes. For example, TOPMARK proposes a system of preformed thermoplastic detectable warnings that is installed in sheets that have a plurality of thermoplastic domes. Unfortunately, the use of thermoplastic warning domes makes the system extremely difficult to install, since heat must be used to install the sheets, but heat will deform or destroy the thermoplastic domes.
My previous U.S. Pat. No. 6,960,989, and the patent that will be issued upon application Ser. No. 10/888,758 describe a system wherein warning domes are encapsulated, covered, or based within thermoplastic prior to field installation. These patents provide a useful reference point for the present invention, and thus are incorporated herein by reference. They do not, however, provide an installation suitable for the most heavy duty use, since the best bonding with the thermoplastic occurs when all surfaces are heated. In addition, thermoplastic looses its dynamic adhesion properties if heated more than once outside of the manufacturing process.
Accordingly, the present invention contemplates application of thermoplastic to the pavement and onto the warning domes at the time of installation onto the recipient pavement surface, which allows heating of all relevant surfaces to create the most effective bond between thermoplastic and other surfaces.
While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.